This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this research is to construct a molecular model of the COPII vesicle cage, a 3-megadalton assembly that encapsulated transport vesicles forming on the endoplasmic reticulum. Through biochemical analysis, we have defined a series of subassemblies of the COPII cage proteins Sec13/Sec31, and we successfully obtained two crystal forms that together constitute the entire assembly unit of the vesicular cage.